Add reverse flag, automatically reverse motor from sensor direction

[SwapnilPande]

This PR updates the behavior of the motorgo with regards to reversing the direction of the motors:

• Adds a reverse flag to the motor_parameters struct (as demonstrated in spin_2_motors.cpp) that allows you to reverse a motor direction
• Uses the detected sensor_direction from the calibration routine to make the motor direction invariant to the way the motor is plugged into a board.

If not reversed, a motor (post-calibration) will always spin counter-clockwise when looking at it from the front. If reversed, the motor will always spin clockwise.

Closes #31 and closes #30

[SwapnilPande]

@stilsota Requesting a review form you. Could you pull the bug-31/ccw-cw-motor-direction branch and see if the motors are behaving as expected?